The alkylation of aromatic compounds with olefins is an established commercial technology. For example, benzene alkylated with short chain (typically 2 to about 6 carbons) hydrocarbons has value as gasoline octane enhancer. Light aromatic compounds alkylated with longer chain (that is, having greater than about 8–10 carbon atoms) linear olefins are commonly sulfonated to produce surfactants suitable for use in detergent manufacture.
The alkylation of benzene and other light aromatic compounds has typically been carried out using hydrofluoric acid or a solid acid catalyst in a fixed bed, plug flow process. For example, U.S. Pat. No. 2,860,173 discloses the use of a solid phosphoric acid as a catalyst for the alkylation of benzene with propylene to produce cumene. More recently, the use of Friedel Crafts catalysts, especially aluminum chloride and certain natural zeolites and synthetic commercial sieves, as alkylation catalysts, has been taught.
Still more recently, alkylation of benzene and light aromatics with C6–C30 olefin co-fed with the aromatic over a solid catalyst bed in a reactive distillation column has been proposed carried out in a reactive distillation column (U.S. Pat. No. 5,770,782).
However, there continue to be problems associated with commercial alkylation processes. For one thing, most of the above processes have practical limits on the amount of aromatic that can be economically co-fed with the olefins, thus resulting in low yields of the desired alkylated products. The typical range for benzene to olefin mole ratio using HF alkylation technology is 4/1 to 8/1. The fixed bed, plug flow solid acid technology referred to above is practiced using a benzene/olefin molar ratio of 15/1 to 30/1. The examples proposed for reactive distillation in U.S. Pat. No. 5,770,782 used a 5/1 to 20/1 benzene/olefin mole ratio for the co-fed mixture and indicate a need for mechanical mixing of the aromatic and olefin before they enter the catalyst bed to assure adequate conversion and alkylate yield.
In addition, all these processes have a significant tendency to produce polysubstituted, in particular, dialkylated aromatics. Solid acid alkylation catalysts tend to deactivate more rapidly in the presence of dialkylated aromatic products. Carbonaceous deposits and heavy organics build up on the catalyst surface, with resultant decrease in catalyst effectiveness and a need to shut the process down to regenerate the catalyst. Most of these problems are directly related to the exothermic nature of the reaction, which has a tendency to be severe and difficult to control. Regeneration is typically provided using benzene maintained in the liquid phase at a pressure of 500 plus psig and temperatures in excess of 250° C.
It is clear that a need exists for a method of alkylation of light aromatics with straight chain olefins that has high olefin conversion rates, a high selectivity for mono-substituted products, and prolonged catalyst effectiveness. Reducing the severity of operating conditions would improve the likelihood of achieving such results.